Frequency modulated (fm) chirp testing for automotive radars using standard automated test equipment (ate) digital pin channels

ABSTRACT

A method for characterizing a FM chirp signal generated by a device under test (DUT) is disclosed. The method comprises receiving a selection of a sample frequency and chirp duration for capturing the FM chirp signal. The method also comprises down converting the FM chirp signal and capturing the FM chirp signal using a digital pin electronics card. The method comprises obtaining a plurality of period measurements from the captured FM chirp signal using a timing measurement unit (TMU) of an automated test equipment (ATE) and converting each of the plurality of period measurements into corresponding frequency values.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit co-pending commonly assigned U.S.Provisional Patent Application Ser. No. 62/141,686, titled “FM CHIRPTESTING FOR AUTOMOTIVE RADARS USING STANDARD ATE DIGITAL PIN CHANNELS”by Roger McAleenan and Robert Bartlett, filed on Apr. 1, 2015, and whichis incorporated herein in its entirety.

FIELD OF THE INVENTION

Embodiments of the present disclosure generally relate to Automatic TestEquipment (ATE) for testing electronic components.

BACKGROUND

Automatic Test Equipment (ATE) is commonly used within the field ofelectronic chip manufacturing for the purposes of testing electroniccomponents. ATE systems both reduce the amount of time spent on testingdevices to ensure that the device functions as designed and serve as adiagnostic tool to determine the presence of faulty components within agiven device before it reaches the consumer.

In general, components, for example, electronic components or devices,micro-electronic chips, memory chips or other integrated circuits (IC),are usually tested before they are delivered to a customer. Testing maybe performed in order to prove and ensure the correct functionalcapability of the devices. The tests are usually performed by means ofan automated test equipment or test system. Examples for such ATE arethe Advantest V93000 SOC for testing system on a chip and system on apackage, the V93000 HSM high speed memory tester (HSM) for testing highspeed memory devices and the Advantest V5000 series. The first is aplatform for testing systems on a chip, systems on a package andhigh-speed memory devices. The latter is for testing memory devicesincluding flash memory and multi-chip packages at wafer sort and finaltest.

During testing these devices under test (DUTs) are exposed to varioustypes of stimulus signals from an ATE. The responses from such devicesunder test are measured, processed and compared to an expected responseby the ATE. Testing may be carried out by automated test equipment,which usually performs testing according to a device specific testprogram or test flow. Such an automatic test system may comprisedifferent drivers for driving certain stimuli to a DUT, in order tostimulate a certain expected response from the device under test.Receiver units of the ATE may analyze the response and generate adesired output regarding the performance of the measured device.

ATE systems can perform a number of test functions on a device undertest (DUT) through the use of test signals transmitted to and comingfrom the DUT. The DUT Interface board is docked to the ATE system by amechanical system that secures board and makes electrical contact using,for example, a interconnect system of pogo blocks and blind mate RF SMPconnectors. An SMP connector offers a frequency range of DC to 40 GHzand is commonly used in miniaturized high frequency coaxial modules. TheATE can interface to and test semiconductor devices in package or waferform.

Conventional ATE systems are very complex electronic systems andgenerally include resources such as digitizers, computers, and digitalcontrol hardware to analyze the signals from the DUT to the testersystem during a session the nearly replicates the real environmentenvisioned for DUT operation. Test signals transmitted from the DUT athigh frequencies are commonly analyzed for the modulationcharacteristics the DUT are capable of providing. Special features maybe incorporated in the design of DUT transmitters that createswept-source or FM (frequency modulated) waveforms that are ramps (up ordown) or saw tooth (both symmetrical and non-symmetrical). The FM chirp(a FM ramp waveform that occurs during a specific time-span) along withother FM waveforms is commonly used in radar (radio detection andranging) applications to mitigate detector bandwidth limits and reducethe cost of the end application like automotive radars. The radarapplication is used to determine a distance or range from thetransmitter to a target, and in automotive applications may alsodetermine speed of the target.

To test the FM chirp signal, typically, high-speed oscilloscopes areused to capture the time domain signal sweeping over frequency. Thismeasurement requires expensive wideband analog hardware, synchronizedmeasurements, and various techniques for the processing (IQ, etc.) tocharacterize a chirp signal to high accuracy. Thus, this technique doesnot lend itself to practical ATE or economical methods for determiningfunctionality and nominal performance.

Further, the analysis and characterization of a FM chirp, which is ahigh speed sweep of frequency over a very short time period (typicallyon the order of 100 micro-seconds) is a difficult and hardware intensivetest because of the challenges involved in simultaneously capturing theswept frequency over the short time periods. Specialized benchequipment, e.g., spectrum analyzers, etc. that may be used are expensiveand impractical for test floor applications in high volume testingenvironments. Further, high performance bench equipment does not lenditself to high volume ATE application work in general because theequipment can be time consuming to use, difficult to set up, requirehighly experienced and educated test floor technicians or may notintegrate well with the ATE hardware. Further, specialized benchequipment such as frequency analyzers occupy a considerable amount ofbench space in the testing environment and do not provide astraightforward method for characterizing the FM chirp signal, e.g.,specialized bench equipment do not provide a visual indication of the FMchirp.

SUMMARY OF THE INVENTION

Accordingly, a need exists for an apparatus and/or method that addressesthe problems with the approaches described above. Using the beneficialaspects of the apparatus and/or method described, without theirrespective limitations, embodiments of the present disclosure providenovel solutions to address these problems.

Embodiments of the present invention provide an apparatus and method fortesting and characterizing FM chirp signals transmitted by a deviceunder test (DUT), wherein the DUT may be a device used in, for example,automotive radar applications. Embodiments of the present inventionreduce the complexity of measuring the FM chirp ramp rates (on a timeaxis) and bandwidth (end to end frequency span of the chirp) byproviding several features, e.g., a visual indication of the FM chirp,the actual frequency sweep relative to the time axis, the deltafrequency increment in a time unit, and a formatted data resultrecording the testing that confirms the FM chirp characteristics inunits of Hz/second (or other equivalent unit, e.g., KHz/microsecond) andthe overall functionality and performance of the DUT FM chirp.

Embodiments of the present invention test and characterize the FM chirpsignal transmitted by a DUT by capturing the chirp with digital pinelectronics having a suitable analog bandwidth at a clock rate based onthe programmed waveform of the FM chirp and a corresponding ramp rate asset by the device under test (DUT). A software process can be employed,in one embodiment, to determine the optimal digital pin settings. Oncethe FM chirp is captured, embodiments of the present invention cancompare the captured results against expected results to determine anyirregularities in performance due to DUT imperfections, e.g., improperbandwidth (the DUT is typically programmed for a specific start and stopfrequency), inaccurate rate (the ramp is expected to complete aprogrammed range in the programmed time), and any non-linearity in theoverall ramp.

In one embodiment, a method for characterizing an FM chirp signalgenerated by a device under test (DUT) is disclosed. The methodcomprises receiving a selection of a sample frequency and chirp durationfor capturing the FM chirp signal. The method also comprises downconverting the FM chirp signal and capturing the FM chirp signal using adigital pin electronics card. The method comprises obtaining a pluralityof period measurements from the captured FM chirp signal using a timingmeasurement unit (TMU) of an automated test equipment (ATE) andconverting each of the plurality of period measurements intocorresponding frequency values.

In another embodiment, a method for characterizing a FM chirp signalgenerated by a device under test (DUT) is disclosed. The methodcomprises receiving a selection of a sample frequency and chirp durationfor capturing the FM chirp signal. Further, the method comprises downconverting the FM chirp signal and capturing the FM chirp signal using adigital pin electronics card to produce a captured FM chirp signal,wherein the capturing comprises capturing samples of the FM chirp signalat a high rate at precise time intervals. The method also comprisesincrementally calculating a frequency range per time interval; andcalculating an average frequency corresponding to each time interval.

In a different embodiment an Automated Test Equipment (ATE) system isdisclosed. The system comprises a memory comprising instructions storedtherein, wherein the instructions are operable to characterize afrequency modulated (FM) chirp signal generated by a device under test(DUT). The system also comprises a processor coupled to the memory, theprocessor configured to operate in accordance with the instructions to:(a) receive a selection of a sample frequency and chirp duration forcapturing the FM chirp signal; (b) down convert the FM chirp signal; (c)capture the FM chirp signal using a digital pin electronics card toproduce a captured FM chirp signal, wherein the digital pin electronicscard is operable to couple with a test-head of the ATE, and wherein thedigital pin electronics card comprise a timing measurement unit (TMU);(d) obtain a plurality of period measurements from the captured FM chirpsignal using the TMU; and (e) convert each of the plurality of periodmeasurements into corresponding frequency values.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification and in which like numerals depict like elements,illustrate embodiments of the present disclosure and, together with thedescription, serve to explain the principles of the disclosure.

FIG. 1 is an exemplary FMCW radar system that generates a linear FMsweep.

FIG. 2 illustrates the FMCW transmitted and detected ramp using thesystem of FIG. 1.

FIG. 3 is an example of a spectrogram.

FIG. 4 is an exemplary digital pin electronic card.

FIG. 5 illustrates exemplary circuitry that can be used to perform thedown conversion of the high frequency signal generated by the DUTtransmitter in accordance with an embodiment of the present invention.

FIG. 6 is a flowchart of an exemplary method of characterizing a FMchirp signal using a TMU device in accordance with an embodiment of thepresent invention.

FIG. 7 illustrates an ideal FM chirp with no errors. The FM chirpillustrated in FIG. 7 is an ideal 100 us ramp that is perfectly linear.

FIG. 8 illustrates a captured FM chirp from a DUT programmed to generatean FM chirp with a bandwidth of 900 MHz and a ramp rate of 100 us inaccordance with an embodiment of the present invention.

FIG. 9 illustrates a captured FM chirp plotted on the same axes as anideal FM chirp in accordance with an embodiment of the presentinvention.

FIG. 10 is a flowchart of an exemplary method of characterizing a FMchirp signal using the digital capture methodology in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the various embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. While described in conjunction with theseembodiments, it will be understood that they are not intended to limitthe disclosure to these embodiments. On the contrary, the disclosure isintended to cover alternatives, modifications and equivalents, which maybe included within the spirit and scope of the disclosure as defined bythe appended claims. Furthermore, in the following detailed descriptionof the present disclosure, numerous specific details are set forth inorder to provide a thorough understanding of the present disclosure.However, it will be understood that the present disclosure may bepracticed without these specific details. In other instances, well-knownmethods, procedures, components, and circuits have not been described indetail so as not to unnecessarily obscure aspects of the presentdisclosure.

As discussed briefly above, in test systems for typical radarapplications, test signals transmitted from the DUT at high frequenciesare commonly analyzed for the modulation characteristics the DUT iscapable of providing. Special features may be incorporated in the designof DUT transmitters to create swept-source or FM (frequency modulated)waveforms that are ramps (up or down) or saw tooth (symmetrical or not).

The FM chirp (a FM ramp waveform that occurs during a specifictime-span) along with other FM waveforms is commonly used in radar(radio detection and ranging) to mitigate detector bandwidth limits andreduce the cost of the end application, e.g., automotive radars. Theradar application is used to determine a distance or range from thetransmitter to a target, and in automotive applications may alsodetermine speed of the target. Chirp signals are a frequency modulationor angle modulation that provides unique capabilities to certain kindsof systems, e.g., radar systems. A chirped or linearly swept frequencyby saw tooth or triangle waveforms is common to provide a range featureto continuous wave (CW) radar. The FM chirp is particular to radarfunctions and takes many forms as required by the application andcorresponding receiver processor. Automotive radar chirp rates, forexample, may be from 40 to 100 microseconds and are FM CW in operation.A pulse radar, for example, may be frequency modulated which provides amethod to resolve targets which are overlapping. The pulse iseffectively coded by FM linear chirps, non-linear, or time-frequencycodes or phase modulation. FM by a chirp of a FMCW radar or within aradar pulse (pulse compression) are examples where measuring the FMcharacteristics is necessary. The FM chirp signal can be broadcasted bya transmitter and the transmitted and/or reflected signal can beanalyzed, for example, for range, speed, and location determination.

A chirped signal is created when a sweep of frequency is made accordingto some function from a starting frequency to an ending frequency. Alinear chirp can be created with a saw tooth waveform, for example, asnoted above. Various delays, dwell times, and similar parameters areused for specific applications. The instantaneous frequency varieslinearly with time. Results of the measurement are commonly given as apercent of ramp or as INL (Integral Non Linearity)/DNL (Differential NonLinearity) ratio.

Ordinary pulsed radar detects the range to a target by emitting a shortpulse and observing the time of flight of the target echo reflection.This requires the radar to have high instantaneous transmit power andoften results in a radar with a large, expensive physical apparatus.Frequency-modulated continuous-wave (FMCW) radars achieve similarresults using much smaller instantaneous transmit powers and physicalsize by continuously emitting periodic signals where the frequencycontent varies with time. A very important type of FMCW radar signal isthe linear FM sweep (wave shape sawtooth or chirp). In this case, therange to the target is found by detecting the frequency differencebetween the received and emitted radar signals. The range to the targetis proportional to this frequency difference, which is also referred toas the beat frequency.

FIG. 1 is an exemplary FMCW radar system that generates a linear FMsweep. The signal is generated by generator 190. The signal passesthrough circulator 191 before being passed to mixer 192 and amplifier193. Loss L1 and L2, as shown in the figure is a measure of theparasitic path losses within the radar electronics. These path lossescontribute to unwanted phase noise in the system that reduce therange/distance the radar is capable of. Finally L3 represents total overthe air loss to/from the target.

FIG. 2 illustrates the FMCW transmitted and detected ramp using thesystem of FIG. 1. Waveform 290 is the main transmitter output with thecorresponding FM chirp ramp shown. Waveform 291 is the radar returnsignal (smaller by L3)-time shifted by the distance to the target andback.

Applications can be characterized as slow-ramp FMCW which means that thewaveform is relatively slow, in milliseconds, and likely consists ofseveral different non-symmetrical ramp shapes. Fast-ramp FMCW consistsof a series of ramps commonly with the same chirp direction (up or down)or triangle waveforms at high repetition rates on the order of hundredsof microseconds. The different applications (in terms of wave shapes)are variously optimized to determine the resolution, distance, and speedin multi-target environments.

Application requirements for automotive radar chipsets have various FMchirp characteristics that are incorporated in the DUT and areprogrammed through the device interface. The waveform shape and durationof the shape are set by internal DUT commands in order to achieve thedesired transmit signal characteristics for the environment anticipated.Selected FM chirps are commonly incorporated into the testing of eachDUT transmitter. Typically, there are requirements that each mode orsetting is tested and recorded against the expected value set by thecontrol programming.

Furthermore, the difficulty in testing each and every ramp possible istime consuming and it is difficult to achieve useful results. High chirprates of the ramp involved, the time resolution required, and the numberof possibilities require a fast and accurate testing approach. Awide-band, high frequency front end is required to handle the highestfrequency expected and a high speed time base that can be synchronized.The time base must sweep fast enough to match the chirp rates with fasttriggering and sequencing with known or minimum delays.

FIG. 3 is an example of a spectrogram. A spectrogram is a visualrepresentation of the spectrum of frequencies in a sound or other signalas they vary with time or some other variable. Spectrograms aresometimes also known as spectral waterfalls. FIG. 3 is a spectrogram ofa non-linear chirp that demonstrates in this case an intentionalnon-linearity. The difficulty of capturing and analyzing chirp signals,the rate (time axis) which is variable, and where a chirp bandwidth (asseen on the y-axis, Fmax−Fmin) is significantly large makes the testingof the characteristics of the chirp important in order to determinewhether the resulting characteristic is intentional or a result of poorperformance of the DUT. As mentioned above, sweeping across a largedifferential in frequency over a very short period of time (on the orderof hundreds of microseconds) is difficult and hardware intensive.

Measurement equipment for FM and specifically for chirped FM applicationrequire some very particular features. Spectrum analyzers captureamplitude versus frequency while oscilloscopes capture amplitude versustime. However, in order to analyze FM chirp signals, a combinationinstrument is desirable that can capture a frequency versus timerepresentation of the signal. Additionally, as noted above, specializedbench equipment, e.g., spectrum analyzers, oscilloscopes etc. that maybe used to capture and analyze FM chirp signals can be expensive andimpractical. For example, a wideband, high frequency front end isrequired to handle the highest frequency expected and a high speed timebase that can be synchronized. Also, the time-base needs to be fastenough to match the chirp rates with fast triggering and sequencing withknown or minimum delays. Some prior hardware solutions have been highspeed one shot digital oscilloscopes and wide band IQreceiver/demodulation. However, all prior techniques employed have usedhigh performance bench equipment that does not lend themselves to ATEapplication work in general because the equipment is time consuming,difficult to set up, and may not integrate well with the ATE hardware.

Accordingly, in order to address the challenges implicit in capturingand analyzing FM chirp signals, embodiments of the present inventionprovide ATE methods to capture, analyze and characterize the FMwaveforms (specifically chirp signals) of transmitters commonlyincorporated in high frequency radar and related applications whereprevious measurement and analysis techniques and equipment had been onlyin bench testing environments. Embodiments of the present inventionprovide an apparatus and method for testing and characterizing DUTtransmitter FM chirp signals and reducing the complexity of measuringthe FM chirp ramp rates (on a time axis) and bandwidth (end to endfrequency span of the chirp) by providing several advantageous features,e.g., a visual indication of the FM chirp, the actual frequency sweeprelative to the time axis, the delta frequency increment in a time unit,and a formatted data result recording the testing that confirms the FMchirp characteristics in units of Hz/second (or other equivalent unit,e.g., KHz/microsecond) and the overall functionality and performance ofthe DUT FM chirp.

Embodiments of the present invention can be implemented in part as asoftware process programmed into the ATE that results in a graphicalsolution for the FM chirp, displaying the captured FM chirp as afunction of the swept frequency over the time axis, which previously wasdifficult and cumbersome to do using other instruments. Embodiments ofthe present invention program the ATE system setups and chirp testprocesses through custom C++ routines and libraries. The C++ compiledcode programs the ATE digital subsystem and executes a series of teststo extract the chirp raw data. The ATE system has additional custom C++code that processes the raw data to calculate and provide a measurementof chirp linearity for the DUT. Embodiments of the present invention canbe programmed and built directly into the ATE hardware so that noadditional bench equipment is required, thereby, making the testingprocess more efficient while saving additional equipment costs. Further,embodiments of the present invention can advantageously increase thetest coverage of existing ATE systems.

Further, embodiments of the present invention test and characterize theDUT transmitter FM chirp. By capturing the chirp with digital pinelectronics having a suitable analog bandwidth at a clock rate based onthe programmed waveform of the FM chirp, a representation of thecorresponding ramp rate set by the device under test (DUT) can bedemonstrated and evaluated.

FIG. 4 is an exemplary digital pin electronic card. It should be notedthat a digital pin card is typically built into an ATE such as AdvantestV93000 SOC that is for testing systems on a chip and systems on apackage. A typical ATE system, e.g., the V93000 will comprise atest-head that can be filled by different pin electronics cards, e.g., adigital pin electronics card. Each digital pin electronics cardtypically contains several measurement channels, wherein each channelcan be used to measure and test high-speed digital I/O interfaces. Thedriver/receiver in the ATE digital pin electronics card can be used, forexample, not only for performing functional tests but also for ACparametric measurements (transition time, jitter, etc.) Further, thedigital pin electronics card can be used for characterizing the DUTtransmitter and for performing functional tests and providing stimulussignals to the DUT receiver. For example, the Advantest Pin Scale (PS)1600 is a type of digital channel card that can be integrated into theV93000 ATE system. The digital pin card typically comprise an integratedtime measurement unit (TMU) that is typically used to extract, measureand compare timing values. The TMU is a type of time to digitalconverter specific to certain ATE systems, e.g., the Advantest 93ksystems. Examples of TMUs can be found, for example, in U.S. Pat. No.8,825,424, titled “Apparatus and Method For Estimating Data Relating toa Time Difference and Apparatus and Method for Calibrating a Delay Line”and U.S. Pat. No. 7,782,242, titled “Time-to-digital conversion withdelay contribution determination of delay elements.”

In one embodiment of the present invention, a software process can beemployed to determine the optimal digital pin settings on the digitalpin card. For example, using the C++ language of the ATE system, a testprogram is written to setup the digital subsystem timing, levels andpattern sequence based on the sampling parameters calculated for thechirp rate and duration. This sequence is executed on the ATE to testthe DUT and extract the raw chirp data set that is used to calculate thelinearity figure of merit.

Once the FM chirp is captured, embodiments of the present invention cancompare the captured results against expected results to determine anyirregularities in performance due to DUT imperfections, e.g., improperbandwidth (the DUT is typically programmed for a specific start and stopfrequency), inaccurate rate (the ramp is expected to complete aprogrammed range in the programmed time), and any non-linearity in theoverall ramp.

The FM chirp capture and analysis technique employed in embodiments ofthe present invention is dependent on suitable external hardware downconverting the expected chirp bandwidth into the digital pinelectronics' bandwidth. For example, the DUT's output may be in the 75to 80 GHz range while the digital pin electronics can only support arange of 1 to 2 GHz. This is accomplished by down converting thetypically high frequency carrier into an intermediate frequency (IF)which is the input to the digital pin electronics.

FIG. 5 illustrates exemplary circuitry that can be used to perform thedown conversion of the high frequency signal generated by the DUTtransmitter in accordance with an embodiment of the present invention.The chirp bandwidth of radar transmitters operating at high microwave ormillimeter frequencies, e.g., signal 590 is matched with the appropriatedigital pin electronics 592 using local oscillator 593. Further, the IFis centered nominally for full bandwidth capture to occur by selectingthe local oscillator frequency so that the chirp bandwidth is mid-bandwith respect to the digital pin electronic's bandwidth. Theimplementation of the down conversion is specific to the devicefrequency of operation and application. The hardware required iscommonly available, e.g., the circuit illustrated in FIG. 5 and is shownonly to address a method of centering the chirp bandwidth A specificadvantage of this approach along with using digital pin electronics withan analog bandwidth matching that of the chirp is that a largerbandwidth can make the measurement easier as the required resolution forthe measurement is less. Dividing down (using digital dividers suitablefor the frequency range) the transmitter frequency reduces the chirpbandwidth by the divide ratio and increases the required time resolutionto make the measurement. A divider would reduce the overall chirpbandwidth while the time duration is unchanged which would be lessdesirable in general and for the present application may unnecessarilyreduce resolution. Down converting the transmitter signal increases thefrequency change observed per sample period

The techniques used in embodiments of the present invention incorporateprecise timing achievable by setting the digital resources to createvery uniform time intervals, as will be described further below. Theresulting time intervals—either as time stamped intervals (the TMUmethod) or records of incremental frequency per time interval (theDigital Capture method)—are then analyzed according to a prescribedprocess using ATE software tools and resources to present a visual—theFM Chirp itself, an analysis of the results to common non-linearityterms like INL and DNL, or other forms.

I. The TMU Sampling Method and Data Analysis Process

Embodiments of the present invention can provide two approaches tocharacterizing the DUT generated FM chirp signal and calculating itsbandwidth and rate. The first approach is a time-stamping method thatreceives the chirp signal from the DUT and uses the TMU of a digital pincard to create time stamps at the selected rate. This rate is determinedusing the expected maximum rate programmed into the DUT. The digital pinelectronics can be programmed to receive the FM chirp signal directlyfrom the DUT transmitter and can use the TMU to characterize and plotthe FM chirp signal as will be detailed below.

The samples are plotted in a fashion that shows the incremental changeof frequency (the ramp bandwidth is sectioned into small time periods)versus the time it takes to complete the ramp. The ramp and digital timestamping are synchronous in that the digital sub-system triggers the FMchirp to start. The maximum bandwidth possible (maximum frequency or endpoint of the ramp) is a function of the digital resources used and howthe bandwidth is positioned in the capture bandwidth. Each digitalresource has a maximum analog bandwidth and maximum sample rate.

Below Table 1 is an exemplary process or pseudo code to determine anadequate resolution bandwidth for the TMU sampling methodology.

TABLE 1 1) Select sampling frequency   i. (Fs in MHz) = 25 MHz(corresponding to Ts = 40 ns) 2) Select FM Chirp duration (FMd) = 100 uS3) Determine Number of samples   i. (Ns) = FMd/Ts = 100e−6/40e−9 = 2,5004) Resolution BandWidth (RBW) = (Fs * 1000000)/Ns = 10 KHz 5) Calculatenumber of input cycles in the coherent sampling window (must be oddnumber of cycles) = (Fin/Fs * Ns) + 1   i. Lower Ramp Frequency = 200MHz Fin      1. (200 MHz/25 MHz * 2500) + 1 = 20001 (# of         signalcycles needed)    ii. Upper Ramp Frequency = 1000 MHz Fin      1. (1000MHz/25 MHz * 2500) + 1 = 100001 (# of         signal cycles needed) 6)Accordingly, 2500 (Ns) @ 25 MHz Fs will cover 200-1000 MHz span in 100us

As seen in the example above, the process for setting up the TMUsampling starts with selecting a sampling rate (Fs), e.g., 2 and a chirpduration, e.g., 100 us (steps 1 and 2), wherein both the sampling rateand chirp duration are selected strategically in order to attain arequired resolution bandwidth (see step 4).

Subsequent to selecting the sampling frequency and chirp duration, thenumber of samples to be obtained is determined at step 3. The resolutionbandwidth can then be obtained using the sampling frequency and thenumber of samples at step 4. If the resolution bandwidth obtained usingthe chosen sampling frequency and chirp duration is not less than therequired or desired chirp resolution, then a different samplingfrequency or chirp duration must be re-selected.

At step 5, the process determines the number of signal cycles needed atthe lower and upper ramp frequencies to ensure coherence in the samplingwindow and prevent the effects of frequency smearing.

FIG. 6 is a flowchart of an exemplary method of characterizing a FMchirp signal using a TMU device in accordance with an embodiment of thepresent invention. As noted above, the TMU device is an integrated timemeasurement unit that is part of a digital pin card in an ATE system(e.g., the Advantest V93k) and is typically used to extract, measure andcompare timing values. For example, the TMU can be programmed to receivea chirp signal from a DUT transmitter and create a time stamp at fixedintervals (e.g., every 40 ns), wherein the time stamp provides a readingof the last measured period of the received chirp signal (the period ofthe signal is measured at multiple times during each 40 ns interval bythe TMU). The period measurement obtained at each time stamp (e.g. every40 ns) can then be used to determine a frequency measurement of thechirp signal at each interval. The frequency measurement can in turn beused to create a plot of the frequency (y-axis) versus the time interval(x-axis).

At step 602, a sample frequency and chirp duration is selected thatprovides the tester with the desired resolution bandwidth (RBW) asdiscussed above. If the RBW is not less than the required chirpresolution, a different sampling rate or chirp duration would need to beselected. For the example illustrated above a sampling frequency of 25MHz and a chirp duration of 100 us is selected.

At step 604, a test chirp signal is down converted and received using adigital pin electronics card from a DUT transmitter. As discussed above,the chirp bandwidth of radar transmitters operating at high microwave ormillimeter frequencies, e.g., signal 590 is matched with the appropriatedigital pin electronics 592 (as shown in FIG. 5).

At step 606, the TMU of an ATE is used to obtain an Ns (2500 in theexample above) number of period measurements of the down converted chirpsignal. The period measurement is the last period measurement obtainedduring the 40 ns interval in between the time stamps. The time scale inthe example above is 0 to 100 us in 40 ns steps. Time step 1 for exampleis 40 ns after the start of the capture and time step 2,500 is 100 usafter the start of the capture.

At step 608, the measurements obtained from the TMU are converted intocorresponding frequency values.

At step 610, the frequency (y-axis) versus time interval (x-axis) isplotted which provides a visual indication of the chirp. Subsequently,the ideal Frequency/Time Interval function can be determined and a timeinterval comparison can be performed to find the largest positive andnegative deviation over the duration and span between the captured chirpand the ideal FM chirp. Also, the worst case deviation can be calculatedas a percentage from the ideal Frequency/Time Interval plot.

FIG. 7 illustrates an ideal FM chirp with no errors. The FM chirpillustrated in FIG. 7 is an ideal 100 us ramp that is perfectly linear.

FIG. 8 illustrates a captured FM chirp from a DUT programmed to generatean FM chirp with a bandwidth of 900 MHz and a ramp rate of 100 us inaccordance with an embodiment of the present invention. The capture inFIG. 8 is performed using 20,000 time stamps generated by a TMU as anexample. The graph shown in FIG. 8 illustrates the FM chirp capture andthe corresponding non-linearity of the ramp generated during the timesweep. As compared with the ideal linear ramp of FIG. 7, FIG. 8 showsthat the ramp tends to be less linear at lower start frequencies ascompared to higher frequencies. Extracting a FM chirp as shown in FIG. 8would be difficult using any other techniques except expensive benchequipment such as an IQ receiver or high speed oscilloscopes and thecorresponding computations would be extensive.

FIG. 9 illustrates a captured FM chirp plotted on the same axes as anideal FM chirp in accordance with an embodiment of the presentinvention. As seen in FIG. 9, the captured FM chirp 992 tends to deviatefrom the ideal FM chirp 991 at the lower and high frequencies.

The recorded results from the capture can then be used to compare theparameters from the perfect ramp to the extracted ramp of the DUT. Forexample, the results can be used to determine the linearity (ornon-linearity) of the captured FM chirp by using a percentage of errorfrom the ideal ramp or an INL/DNL report. As mentioned above, severalmethods evaluate results: a graphical approach (plotting the minimum tomaximum frequency over the expected ramp rate); an IncrementalNon-Linearity/Differential Non-Linearity (INL/DNL) report; a derivativeplot showing the minimum and maximum deviation from the expected ramprate. Further, a time interval comparison can be performed to find thelargest positive and negative deviation over the duration and spanbetween the captured chirp and the ideal FM chirp. Also, the worst casedeviation can be calculated as a percentage from the idealFrequency/Time Interval plot.

In comparing the captured ramps to the expected parameters, a figure ofmerit can be obtained in a relatively quick manner using standard ATEdigital resources where previously, the cost of the resources (forexample a high speed oscilloscope or spectrum analyzer) and theincorporation of that capital into the ATE environment would beprohibitive. The testing provides a production method to assure that theramp performance is meeting some metric without having to incorporatebench type equipment for an equivalent result.

II. The Digital Capture Sampling Method and Data Analysis Process

The Digital Capture Sampling methodology can be employed where the ATEor digital pin electronics card does not have a TMU device that canprovide precise period measurements at predetermined intervals. TheDigital Capture Sampling method approach is a more extensive techniquewhere a predefined capture rate is set on a digital channel such thatthe incremental frequency change per sample is fine enough to provide aresolution sufficient to expose linearity errors in the waveform. Eachincremental time period is analyzed to determine the actual change inincremental frequency during that interval. Successive intervals arecaptured and then analyzed. Several methods can be used to evaluateresults: a graphical approach (plotting the minimum to maximum frequencyover the expected ramp rate); an Incremental Non-Linearity/DifferentialNon-Linearity (INL/DNL) report; a derivative plot showing the minimumand maximum deviation from the expected ramp rate.

Below Table 2 is an exemplary process or pseudo code to determine anadequate resolution bandwidth for the digital capture samplingmethodology.

TABLE 2 1) Select Sampling frequency   i. (Fs in MHz) = 800 MHz(corresponding to      Ts = 1.25 ns) 2) Select FM Chirp duration(FMd) =100 us 3) Determine Number of samples(Ns)   i. FMd/Ts = 100e−/1.25e−9 =80,000 4) Resolution Band Width(RBW) =(Fs * 1000000)/Ns = 10 KHz 5)Calculate number of input cycles in the coherent sampling window (mustbe odd number of cycles) = (Fin/Fs * Ns) + 1   i. Lower Ramp Frequency =200 MHz Fin      1. (200 MHz/800 MHz * 80000) + 1 = 20001 (# of        signal cycles needed)    ii. Upper Ramp Frequency = 1000 MHz Fin     1. (1000 MHz/800 MHz * 80000) + 1 = 100001 (# of         signalcycles needed) Accordingly, 80,000(Ns) @ 800 MHz Fs will cover 200-1000MHz span in 100 us

As seen in the example above, the process for setting up the digitalcapture methodology starts with selecting a sampling rate (Fs), e.g., 2and a chirp duration, e.g., 100 us (steps 1 and 2), wherein both thesampling rate and chirp duration are selected strategically in order toattain a required resolution bandwidth (see step 4). The sampling ratefor the digital capture method is a lot higher than the TMU method.

Subsequent to selecting the sampling frequency and chirp duration, thenumber of samples to be obtained is determined at step 3. The resolutionbandwidth can then be obtained using the sampling frequency and thenumber of samples at step 4. If the resolution bandwidth obtained usingthe chosen sampling frequency and chirp duration is not less than therequired or desired chirp resolution, then a different samplingfrequency or chirp duration must be re-selected.

At step 5, the process determines the number of signal cycles needed atthe lower and upper ramp frequencies to ensure coherence in the samplingwindow and prevent the effects of frequency smearing.

FIG. 10 is a flowchart of an exemplary method of characterizing a FMchirp signal using the digital capture methodology in accordance with anembodiment of the present invention. The digital capture testing methodcalculates ramp performance by capturing samples at a high rate withprecise time periods and then incrementally calculating frequency rangeper time interval.

At step 1002, a sample frequency and chirp duration is selected thatprovides the tester with the desired resolution bandwidth (RBW) asdiscussed above. If the RBW is not less than the required chirpresolution, a different sampling rate or chirp duration would need to beselected. For the example illustrated above a sampling frequency of 800MHz and a chirp duration of 100 us is selected. Each sample interval is1.25 ns in time from the start of the capture. As shown above, 80,000samples are obtained at intervals of 1.25 ns.

At step 1004, a test chirp signal is down converted and received using adigital pin electronics card from a DUT transmitter. As discussed above,the chirp bandwidth of radar transmitters operating at high microwave ormillimeter frequencies, e.g., signal 590 is matched with the appropriatedigital pin electronics 592 (as shown in FIG. 5).

At step 1006, a frequency value for each interval can be obtained bydetermining the number of zero crossings the captured signal experiencesduring a respective time interval. Further, a Fast Fourier Transform(FFT) is performed on each 1 us sub interval sample set, wherein a 100us chirp duration (from the example above) results in a total of 100 subinterval sample sets.

At step 1008, the average frequency is calculated for each sub intervalsample sets resulting in a total of 100 average frequencies for a 100 uschirp duration.

At step 1010, the frequency (y-axis) versus time interval (x-axis) isplotted which provides a visual indication of the chirp. Subsequently,the ideal Frequency/Time Interval function can be determined and a timeinterval comparison can be performed to find the largest positive andnegative deviation over the duration and span between the captured chirpand the ideal FM chirp. Other methods can be used to evaluate results:an Incremental Non-Linearity/Differential Non-Linearity (INL/DNL)report; a derivative plot showing the minimum and maximum deviation fromthe expected ramp rate calculated as a percentage from the idealFrequency/Time interval plot.

The digital capture methodology results in a similar characterization ofthe FM chirp as the TMU methodology. The major difference between themethodologies is that the TMU method allows a more direct measurement ofthe frequencies while the digital capture method involves capturingsample at high rates with precise time periods and incrementallycalculating a frequency range per time interval using FFTs.

While the foregoing disclosure sets forth various embodiments usingspecific block diagrams, flowcharts, and examples, each block diagramcomponent, flowchart step, operation, and/or component described and/orillustrated herein may be implemented, individually and/or collectively,using a wide range of hardware configurations. In addition, anydisclosure of components contained within other components should beconsidered as examples because many other architectures can beimplemented to achieve the same functionality.

The process parameters and sequence of steps described and/orillustrated herein are given by way of example only. For example, whilethe steps illustrated and/or described herein may be shown or discussedin a particular order, these steps do not necessarily need to beperformed in the order illustrated or discussed. The various examplemethods described and/or illustrated herein may also omit one or more ofthe steps described or illustrated herein or include additional steps inaddition to those disclosed.

It should also be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as may be suited to theparticular use contemplated.

Embodiments according to the invention are thus described. While thepresent disclosure has been described in particular embodiments, itshould be appreciated that the invention should not be construed aslimited by such embodiments, but rather construed according to the belowclaims.

What is claimed is:
 1. A method for characterizing a frequency modulated(FM) chirp signal generated by a device under test (DUT), the methodcomprising: receiving a selection of a sample frequency and chirpduration for capturing the FM chirp signal; down converting the FM chirpsignal; capturing the FM chirp signal using a digital pin electronicscard to produce a captured FM chirp signal; obtaining a plurality ofperiod measurements from the captured FM chirp signal using a timingmeasurement unit (TMU) of an automated test equipment (ATE); andconverting each of the plurality of period measurements intocorresponding frequency values.
 2. The method of claim 1, wherein thesample frequency and the chirp duration are selected to obtain a desiredresolution bandwidth, and further comprising: characterizing thecaptured FM chirp signal by analyzing the frequency values versuscorresponding time values.
 3. The method of claim 1, further comprising:creating a visual indication of the captured FM chirp signal by plottingthe frequency values versus corresponding time values on a display unit.4. The method of claim 3, further comprising: calculating a deviation ofthe captured FM chirp signal from an ideal FM chirp signal.
 5. Themethod of claim 1, wherein the sample frequency and chirp duration areselected, wherein a resultant resolution bandwidth is less than apredetermined required chirp resolution value.
 6. The method of claim 1,wherein the sample frequency and the chirp duration are selected basedon an expected maximum transmit rate programmed into the DUT.
 7. Themethod of claim 1, wherein the plurality of period measurements areobtained at predetermined time intervals over the chirp duration.
 8. AnAutomated Test Equipment (ATE) system, the system comprising: a memorycomprising instructions stored therein, wherein the instructions areoperable to characterize a frequency modulated (FM) chirp signalgenerated by a device under test (DUT); a processor coupled to thememory, the processor configured to operate in accordance with theinstructions to: receive a selection of a sample frequency and chirpduration for capturing the FM chirp signal; down convert the FM chirpsignal; capture the FM chirp signal using a digital pin electronics cardto produce a captured FM chirp signal, wherein the digital pinelectronics card is operable to couple with a test-head of the ATE, andwherein the digital pin electronics card comprise a timing measurementunit (TMU); obtain a plurality of period measurements from the capturedFM chirp signal using the TMU; and convert each of the plurality ofperiod measurements into corresponding frequency values.
 9. The systemof claim 8, wherein the sample frequency and the chirp duration areselected to obtain a desired resolution bandwidth, and wherein theprocessor is further configured to operate in accordance with theinstructions to: characterize the captured FM chirp signal by analyzingthe frequency values versus corresponding time values.
 10. The system ofclaim 8, wherein the processor is further configured to: create a visualindication of the captured FM chirp signal by plotting the frequencyvalues versus corresponding time values on a display unit associatedwith the ATE.
 11. The system of claim 10, wherein the processor isfurther configured to: calculate a deviation of the captured FM chirpsignal from an ideal FM chirp signal.
 12. The system of claim 8, whereinthe sample frequency and chirp duration are selected, wherein aresultant resolution bandwidth is less than a predetermined requiredchirp resolution value.
 13. The system of claim 8, wherein the samplefrequency and the chirp duration are selected based on an expectedmaximum transmit rate programmed into the DUT.
 14. The system of claim8, wherein the plurality of period measurements are obtained atpredetermined time intervals over the chirp duration.
 15. A method forcharacterizing a FM chirp signal generated by a device under test (DUT),the method comprising: receiving a selection of a sample frequency andchirp duration for capturing the FM chirp signal; down converting the FMchirp signal; capturing the FM chirp signal using a digital pinelectronics card to produce a captured FM chirp signal, wherein thecapturing comprises capturing samples of the FM chirp signal at a highrate at precise time intervals; incrementally calculating a frequencyrange per time interval; and calculating an average frequencycorresponding to each time interval.
 16. The method of claim 15, whereinthe sample frequency and the chirp duration are selected to obtain adesired resolution bandwidth, and further comprising: characterizing thecaptured FM chirp signal by analyzing the frequency values versuscorresponding time values.
 17. The method of claim 15, furthercomprising: creating a visual indication of the captured FM chirp signalby plotting the average frequency versus corresponding time values on adisplay unit.
 18. The method of claim 15, further comprising:calculating a deviation of the captured FM chirp signal from an ideal FMchirp signal.
 19. The method of claim 15, wherein the calculating afrequency range comprises calculating a Fast Fourier Transform (FFT) oneach time interval.
 20. The method of claim 15, wherein the samplefrequency and the chirp duration are selected based on an expectedmaximum transmit rate programmed into the DUT.